Design methods that consider the complete physical system (human interfaces and functional capacities of human interfaces) and incremental distinctions in humans are not widely applied. Human beings vary from a cognitive and physical standpoint. Manufacturing approaches have attempted to implement mass customization to provide end users with personalized products. However, these approaches are limited since (1) mass customization is orthogonal to human variability and (2) manufacturing costs are increased, through additional time and parts, required when mass-producing customized products. This research facilitates the integration of traditional engineering performance metrics and biomechanics creating manufacturable innovations in customized design that target population accommodation. The present method captures (1) human and product interface interactions, (2) interaction accommodation, (3) the impact of interaction accommodation on engineering performance metrics (thermal, structural, fluid, reliability, etc.), and (4) number of products required to accommodate the population. Engineering design techniques provide a structured method for reducing product and performance metrics which provide the foundational framework for the optimization model(s) integrating this method. Optimization enables optimal performance metrics constrained by population accommodation, producing the product metrics and the number of products required to accommodate the population. This work is a novel approach for addressing complex questions for interaction variability in mass production targeting population accommodation while maintaining product performance, which facilitate addressing larger problems of mass customization in mass production.